Thermal cooling wraps or packs are well known in the art for providing any manner of therapeutic or soothing cooling to a person. For example, such devices are typically used to treat sports injuries, or used in various medical procedures to cool a patient. Conventional self-contained cooling packs are available that contain particles of a cooling agent, such as urea or ammonium nitrate, separated from a compartment or pouch that contains an aqueous liquid. Typically, the cooling function is achieved by breaking or rupturing a barrier or seal between the liquid and cooling agent particles. As the particles dissolve in the aqueous liquid, heat is absorbed and a cooling effect is generated. Such devices are widely used in the medical industry, and in the transport and storage of food products.
U.S. Pat. No. 6,099,555 describes a gelling cold pack that includes a gelling agent, such as starch, adhered as a liquid permeable non-continuous coating to a composite particulate “cold-generating” material that interacts with a liquid to produce cold. The cold-generating material may be one of a number of ammonium salts, tin, cobalt or nickel salts, alkali metal salts, or an organic compound such as urea. The gelling material is applied to the cold-generating particles by spraying, dipping, brushing or with the use of an adhesive material. The coated particles are housed in liquid-impermeable, heat-conducting zones of a disposable container, with at least one other zone containing a liquid. The cold pack is activated by rupturing a frangible membrane between the zones. These and similar cold packs are designed to be placed into containers to cool food or drinks. Such cold packs also have a number of medical applications, including therapeutic devices for relief from overheating, wound care, treatment of strained muscles, joints or ligaments, or to treat or prevent heat exhaustion.
U.S. patent application 2005/0136765 describes various fibrous sheet materials, such as tissue and paper towels, provided with chemical agents, such as certain salts, that create a temperature change in the sheet when exposed to water. When water is absorbed by the sheet, the salt dissolves and produces a cooling or warming temperature change depending on the particular salt. The sheets may be used for wiping the hands, face, and body since the temperature change can be initiated by absorption of body fluids, such as sweat or surface moisture on the skin.
WO 2004/105709 describes various types of self-warming skin care compositions that include a heat generating powder coated with a combination of oils and/or waxes to partially delay the onset of the exothermic reaction and extend the duration of the warming effect. The heat generated in the exothermic reaction of the powder with water warms the skin, enhances cleansing, and may provide improved blood circulation. The heat generating powder may be an inorganic salt, such as calcium chloride, magnesium chloride, magnesium sulphate, and the like.
Unfortunately, various problems arise when attempting to apply an endothermic or exothermic composition to a substrate. Specifically, if the composition were exposed to moisture during application or storage, the reaction could occur prematurely. Certain salts are susceptible to absorbing moisture from the air and may slowly warm or cool over time until an equilibrium moisture state is reached. This ultimately would lower the quality of the composition and degrade the desired effect of any device incorporating the composition. Also, it is difficult to apply the compositions to substrates in an effective and uniform concentration that yields the desired result, particularly a sustained and controlled reaction as compared to a rapid, short duration temperature change.
As such, the art is continuously seeking improved thermal cooling devices that are simple, effective, relatively inexpensive to make, and produce a controlled and sustained cooling effect.